1. Field of the Invention
The present invention relates to an all-solid battery and a method of manufacturing the all-solid battery, and particularly relates to an all-solid lithium ion battery and a method of manufacturing the all-solid lithium ion battery.
2. Related Art
In an all-solid battery, in which an inorganic solid electrolyte is used, and an organic compound is not even used in an electrode, there is no risk of liquid leakage and gas generation; therefore, the all-solid battery is expected to be a safe battery. Moreover, as compared to a liquid-based battery, the all-solid battery is rare for a reaction other than a cell reaction to occur, and thus it is expected that the life of the battery can be extended.
Furthermore, in a case in which a sintered body is used as an inorganic solid electrolyte, a method is used, in which an inorganic solid electrolyte precursor and an electrode precursor are laminated, and these are calcined at the same time, a result of which a sintered body of an electrode and a solid electrolyte can be prepared, and the interface can be preferably joined. In this method, while manufacturing cost is reduced by reducing manufacturing processes, reduction of ionic migration resistance can be expected in the interface where the electrode layer and the solid electrolyte layer have been joined.
However, in a lithium ion battery having a particularly high electromotive force, a positive electrode is composed of materials with a high oxidizing power, and a negative electrode is composed of materials with a high reducing power.
Therefore, in a case in which these materials and a solid electrolyte are calcined at the same time, a problem is likely to occur in which, in the interface between a solid electrolyte layer and an electrode layer, a reaction between the two layers would generate chemical compounds that inhibit ionic conduction. In addition, in order to impart ionic conductivity in an electrode, an electrode precursor preferably contains an electrode active material powder and a solid electrolyte powder. However, even in a grain boundary between these powders, chemical compounds that do not contribute to a cell reaction, and chemical compounds that inhibit ionic conduction may be generated due to a reaction during calcination. Therefore, even if an interface between the electrode layer and the solid electrolyte layer is joined well by calcination, lithium ionic migration resistance is increased due to chemical compounds generated in the interface between the electrode layer and the solid electrolyte layer and in a grain boundary between the electrode active material and the solid electrolyte in the electrode layer; therefore, charge and discharge at a high current will not be realized after all.
Furthermore, even in a case in which chemical compounds that inhibit ionic conduction are not generated, if electrical conductivity of an electrode active material itself is low, supply and emission of electrons are not performed well in the electrode active material; therefore, charge and discharge at a high current would not be realized, either.
In order to solve such problems, a method has been proposed in which a low temperature is employed as a calcination temperature; however, since sintering of an electrode and a solid electrolyte is insufficient in such a method, charge and discharge at a high current have not been realized.
Patent Document 1 proposes a method, in which a low-oxygen atmosphere is used as an atmosphere for calcining a laminate composed of an electrode precursor, a solid electrolyte precursor, etc. However, a battery manufactured by this method merely performs charge and discharge at an extremely small current of 0.88 μA/cm2; therefore, charge and discharge at a high current have not been realized.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-227362